- Biopsy samples cannot be taken with a virtual colonoscopy, and polyps cannot be removed as they can during a standard colonoscopy.
A colonoscopy is considered the gold standard as a screening test for colon cancer. The test requires the insertion of a long flexible viewing tube—a colonoscope—through the entire colon and, at times, the lower portion of the small intestine. By means of the colonoscope, a gastroenterologist can view the inside of the colon and also take biopsy samples and remove any abnormal growths that may develop into colon cancer.
Although patients undergoing colonoscopy are sedated, colonoscopy can cause abdominal cramping, bloating, and a need to pass gas. Patients must also wait until the sedation wears off, which can take an hour, and someone must drive them home. Serious complications of colonoscopy are rare, but can include perforation of the colon.
It is understandable that a “virtual” colonoscopy—a relatively new technology—sounds more appealing. Patients are not sedated, and the procedure is much less invasive. A tube is inserted into the patient’s rectum and the colon is filled with air so that its entire length can be viewed using computed tomography (sometimes called a CT or CAT scan).
However, patient preparation is the same as it is for a conventional colonscopy: A mainly liquid diet must be followed for up to three days before the colonoscopy and a strong laxative must be taken the evening prior to the test to ensure the colon is cleansed for viewing. And although virtual colonoscopy is quicker, safer, and cheaper than traditional colonoscopy—and nearly as accurate in detecting “clinically relevant” polyps—a number of drawbacks make virtual colonoscopy an undesirable option for most people.
For example, biopsy samples cannot be taken with a virtual colonoscopy. If any abnormalities are detected, patients still require a standard colonoscopy for confirmation of the diagnosis. In addition, polyps cannot be removed as they can during a standard colonoscopy. Also, in a survey of screenings at nine major hospitals, virtual colonoscopy proved significantly less capable than standard colonoscopy of detecting small polyps (6 mm or less).
In the future this test will be most useful for people at low risk for colon cancer. Currently, a virtual colonoscopy is not recommended for routine colon cancer screening purposes. You are an appropriate candidate for virtual colonoscopy only if you have a medical condition that makes a standard colonoscopy risky or physically difficult.
